I encountered a problem recently. I downloaded the textures and put them in the document. Then, I ran Space Engine. Before I entered the main theme, it showed that it was loading textures. After I entered the software and landed on planets such as Earth or Mars, I couldn't see the textures. The surfaces of planets are seemed to be the same before I downloaded textures. How can I solve this problem?

You can go to options and increase the number of detail, also the textures don't do much of a change you can notice it if you zoom more into the planet itself but at long distance it pretty much looks the same.